WO 2015/107063 A1 has disclosed such a method and system, and such a computer program.
In order to fit the spectacle lenses correctly into a spectacle frame, it is necessary to determine so-called fitting parameters so that the optical centers of the lenses can be made to coincide with the visual axes of the corresponding eyes in order thus, for example, to know information about the interpupillary distance and the information about the level of the pupils in relation to the spectacle frame. Moreover, it is important to determine the level of the optical centers of the spectacle lenses in relation to the upper or lower edge of the spectacle frame, into which the spectacle lenses are inserted.
By way of example, fitting parameters can be determined by virtue of an optician and a subject sitting or standing opposite one another, with the subject wearing the frame of his choice with a support lens held therein. The subject is asked to look into the distance and the optician then indicates the visual point with a cross on the lens or on a contact line foil according to appearance, as identified when looking at one another. This cross (centering cross) then determines the position of the optical center of the spectacle lens to be inserted into the frame. This method is carried out individually for each eye of a subject. The distance between the centering crosses established in this manner is the interpupillary distance PD.
U.S. Pat. No. 6,659,609 has described a system for determining fitting parameters for spectacle lenses which contains a digital camera accommodated on a column in a height-adjustable manner, the lens of which camera being arranged in the region of the front surface of the housing, together with a mirror and a light source. This system comprises a computer linked to the digital video camera, the computer determining fitting parameters for the spectacle frame by image evaluation of the image of a subject with a spectacle frame and a measurement bracket fastened to the spectacle frame. For the purposes of determining the fitting parameters, the subject is asked in this case to look directly into the digital camera, with the optical axis of the camera having to be parallel with the viewing direction of the subject. As an alternative thereto, provision can also be made for displacing the camera in order to ensure that the image plane of the camera is parallel with the plane of the measurement frame and the image of the eyes of the subject is then centered in the image plane of the camera in relation to the optical axis thereof.
United States patent application publication 2010/0195045 A1 has described a method for determining spectacle lens fitting parameters, in which the sought-after fitting parameter is determined by means of image analysis from the image of a subject wearing spectacles with a measurement bracket fixed thereon, which image was acquired by a camera. In this case, the subject is asked to look at an LED attached to the camera. The camera contains an inclination sensor in order thereby to determine the inclination angle of the optical axis of the camera in relation to the horizontal. The camera emits a warning signal if the inclination angle acquired by means of the inclination sensor exceeds a threshold. This ensures that the optical axis of the camera always intersects the frame plane of the spectacle frame approximately perpendicularly during the image recording. What this achieves is that a parallax error caused by the distance of the eyes of the subject from the frame plane is negligible when determining fitting parameters. In the case where the frame plane is not parallel to the image plane of the camera, United States patent application publication 2010/0195045 A1 proposes a computational image correction in order thereby to compensate an image distortion caused by this recording situation.